47. Arthonia] 14. ARTHONIACEAE 89 



51. Arthonia taedescens Nyl., in Willey, Syn. Arth. 30. 1890. 



Superficial thalius thin, greenish gray, smooth, inconspicuous; apothecia minute, 

 0.1-0.2 mm. across, irregular to elongated, sometimes branched, partly immersed 

 to adnate, the disk flat to convex, black; tinged light brown within; spores fusi- 

 form-ovoid, 1-septate, 19-26 X 7.5-9 /x. 



On bark, Virginia, Louisiana, Florida, and Alabama. 



52. Arthonia subminutissima Nyl., Flora 68:448. 1885. 



Superficial thalius thin, ashy white, smooth; apothecia very minute, 0.06-0.13 

 mm. across, or reaching 0.3 mm. long, adnate, round to oblong, the disk flat, black; 

 hyaline within; asci pyriform; spores hyaline, oblong-ovoid, 1-septate, one cell 

 larger, 7-9 X 2.5-3 tt. 



On trees, Massachusetts. 



53. Arthonia microspermella Willey, Syn. Arth. 31, 32. 1890. 



Thalius very thin to thin, widespread, dirty white; apothecia minute, 0.1-0.2 

 mm. across or reaching 0.4 mm. in length, irregular to somewhat elongated, some- 

 times more or less branched, the disk flat, brownish black to black, lighter when 

 wet; hypothecium hyaline; spores hyaline, ovoid, 1-2-septate, 10-14 X 3.5-5 /a. 



On trees, Texas and California. 



54. Arthonia luridoalba Nyl., in Willey, Syn. Arth. 36. 1890. 



Superficial thalius thin, ashy white, smooth to slightly rough; apothecia small, 

 0.2-0.6 mm. across, partly immersed to adnate, round to angular, or oblong and 

 reaching 1 mm. long, the disk flat to convex, lurid blackish; hypothecium darker; 

 hymenium pale brownish; spores hyaline, oblong-ovoid, 3-septate, 12-15 X 5-6 /x. 



On trees, New Hampshire. 



55. Arthonia diffusa Nyl., Flora 68:448. 1885. 



Superficial thalius thin, ashy white, rough, becoming scurfy and sometimes dis- 

 appearing; apothecia minute to small, 0.2-0.8 mm. across, basally immersed to 

 adnate, round to slightly irregular, the disk flat to convex, black to whitish prui- 

 nose; hyaline within; spores hyaline, oblong-ovoid, 3-septate, one end cell often 

 larger, 8-12 X 3-4.5 ii. 



On trees, northern United States east of the Mississippi River. 



56. Arthonia diffusella Fink; Hedrick, Mycologia 25:310. 1933. 



Thalius thin, smooth to slightly rough, dull white to ashy; apothecia minute to 

 small, 0.1-0.3 mm. across, round to more frequently irregular, solitary or rarely 

 clustered, partly immersed to adnate, the disk flat to slightly convex, black; hy- 

 pothecium brownish; asci subpyriform; spores 8, hyaline, 1-3- usually 2-septate, 

 constricted at the septa with one or two upper cells commonly larger, 1 2-1 5 X 

 3.5-4 fi, irregularly arranged. 



On old wood, Minnesota and Michigan. 



57. Arthonia subdiffusa Willey, Syn. Arth. 3o. 1890. 



Superficial thalius thin, ashy white, smooth, becoming obscurely powdery; 

 apothecia minute, 0.07-0.15 mm. across, adnate, round to slightly irregular or 

 oblong, the disk flat to convex, black; hyaline within; asci pyriform; spores hyaline, 

 ovoid-ellipsoid, 3-septate, 13-17 X 4-5 /x. 



On trees, Florida and southern California. 



58. Arthonia melaspora Tuck., in Willey, Int. Stud. Lich. Suppl. 54. 1887. 

 Superficial thalius thin, white-powdery ; apothecia minute to small, 0.05-0.2 



mm. across, immersed, round to irregular or oblong, becoming 0.6 mm. long, the 

 disk flat, whitish pruinose to blackish; tinged light brownish within; spores dark 

 brown, oblong-ovoid, 3-5-septate, one end cell larger and darker in color, 23-26 X 

 10-12 /x. 



On old wood, Florida. 



